A typical cellular radio access system includes a radio access network (RAN) that is arranged to provide mobile stations with access to one or more transport networks such as the public switched telephone network (PSTN) and/or the Internet. The RAN may include a cellular base station (e.g., base transceiver station, access node, eNodeB, or the like), which itself may include an antenna configuration and associated equipment for radiating to define one or more coverage areas in which a mobile station can wirelessly communicate with the base station over an air interface. The cellular radio access system may further include various entities such as switches, gateways, and controllers that may facilitate connectivity with a transport network and/or may help control aspects of RAN operation such as registration and de-registration of mobile stations. For example, the cellular radio access system could include a mobile switching center (MSC), a mobility management entity (MME), a soft-switch, a media gateway controller (MGC), a packet data serving node (PDSN), a serving gateway (S-GW), and a packet data network gateway (P-GW). Further, these entities may be coupled with a signaling network to facilitate communication with other system entities such as a home location register (HLR) (e.g., a home subscriber server (HSS)) or a location-determination system, among other entities.
In practice, when a mobile station enters into coverage of the RAN, such as coverage of a base station, the mobile station may engage in a registration (e.g., attach) procedure so as to then be able to engage in bearer-data communication, perhaps to place and receive calls and engage in wireless packet-data communication, to the extent that the mobile station's service profile and capabilities allow, perhaps. During the registration procedure, the mobile station may transmit a radio-access-registration-request (e.g., attach-request) message via an air-interface uplink channel to the base station providing the coverage area. Upon receiving that registration-request message, the base station may signal to one or more other entities of the cellular radio access system, such as an MSC or MME as examples, which in turn may signal to the HLR.
After initially registering in a coverage area, a mobile station may continue to monitor the pilot signal of that coverage area as well as the pilot signals of adjacent coverage areas, and may at some point transmit to the serving base station a radio measurement report (e.g., pilot-strength-measurement message or data-rate-control message) indicating the strength of the monitored signals. If the base station determines based on such a message that an adjacent coverage area provides sufficiently stronger coverage than the currently serving coverage area, the base station may arrange for a handoff of the mobile station to the adjacent coverage area.